Radiation attenuation properties of chemically prepared MgO nanoparticles/HDPE composites

Sheets of high-density polyethylene (HDPE) loaded with magnesium oxide in micro and nano were synthesized with different weight percentages of micro-MgO (0,5,10,20 and 30% by weight) and nano-MgO (5 and 30%) and shaped in form of disc and dog bone shape. The morphological, mechanical, and attenuation characteristics of each concentration were determined. The linear attenuation coefficients (LAC) of the prepared discs were calculated using a well-calibrated scintillation detector and five standard gamma-ray point sources (241Am, 133Ba, 137Cs, 60Co and 152Eu). The LAC was theoretically calculated for HDPE/micro-MgO composites using XCOM software. A good agreement between the theoretical and experimental results was observed. The comparison between micro and nano-MgO as a filler in HDPE was evaluated. The results proved that the loaded nano-MgO in different proportions of HDPE produced greater attenuation coefficients than its micro counterpart. The addition of nano MgO with different weight percentage led to a significant improvement in the mechanical properties of HDPE, the ultimate force and ultimate stress increased as the concentration of nano MgO increased, and the young modulus of HDPE also increased with increasing concentration of micro and nano MgO.


Scientific Reports
| (2023) 13:9945 | https://doi.org/10.1038/s41598-023-37088-y www.nature.com/scientificreports/ The main target of this study was to use micro-sized magnesium oxide, nano-sized magnesium oxide, and HDPE to prepare composites in the form of sheets by the compression molding method to get experimental data for the attenuation of photons through these composites at different energies as well as changes in their mechanical properties.

Materials and methods
Samples preparation. A commercial HDPE as a matrix was obtained by Sidi Kerir Petrochemicals Company (sidpic), HD5403EAgrade with an index of melting flow point of 0.35 g/min and a density of 0.955 g/cm 3 . MgO microparticles in the powder phase were purchased from the Loba Company for laboratory reagents and fine chemicals (India) without further purification. EDX of the purchased MgO is shown in Fig. 1.
Mgo nanoparticles preparation. Magnesium oxide nanoparticles were synthesized using magnesium nitrate (MgO 3 H 12 O 6 ) as source material with sodium hydroxide and all chemicals were used without extra purification. For the typical experimental procedure, 0.2 M magnesium nitrate hydrated (MgO 3 H 12 O 6 ) was dissolved in 100 ml of deionized water. A 0.5 M sodium hydroxide solution was added dropwise to the prepared magnesium nitrate solution while stirring it continuously. A white precipitate of magnesium hydroxide appeared in a beaker after a few minutes. The stirring continues for 30 min. The pH of the solution is 12 as measured by the pH paper. pH is one of the crucial parameters in determining the outcome of any synthesis process 20 . The precipitate was filtered and washed with methanol three times to remove ionic impurities. Samples were annealed at 100 °C for two hours, then the white powder undergoes a solid state reaction at a temperature of 500 °C for 4.5 h. The structure of the synthesized MgO nanoparticles was investigated using X-ray diffraction, XRD (X-ray Powder Diffraction-XRD-D2 Phaser, Bruker, Germany). Figure    Synthesis of composite sheets. The composites were prepared by using the compression molding method for the following samples (0 wt%, 5 wt%, 10 wt%, 20 wt% and 30 wt% ) of micro magnesium oxide/ HDPE and (5wt% and 30wt% ) of Nano HDPE/MgO. Firstly, we used an electric balance of sensitivity 0.0001 g to weigh HDPE and fillers. In order to prepare the composite sheets, HDPE was placed between two roll mills at a temperature of 185 °C to make sure that it was completely melted (which is higher than the melting point of HDPE 134 °C) for 18 min with the rotation speed of 40 rpm. MgO powder was added gradually with continuous rolling for 10 min to obtain a uniform distribution of powder in HDPE. The completely mixed sample was placed in an iron frame of dimensions (12.5 × 12.5 × 0.3 cm 3 ) then, the samples were compressed by the hydraulic press at a pressure 10 Mpa and a temperature 185 °C for 15 min, the pressure was raised gradually to 20 Mpa through 15 min. The sample was kept under pressure for 30 min to cool down gradually to a temperature of 50 °C then, the resultant sheets were cut into circular disks of a diameter of 8 cm for micro and 2.5 cm for Nano to do radiation investigation. For structural analysis of the composites and in order to confirm the presence of Mgo nanoparticles in the matrix of HDPE, FTIR (Bruker Tensor 37 FT-IR, Bruker, Germany) study was carried out. FTIR spectra of the 5wt% and 30wt% of Nano HDPE/MgO composite are shown in Fig. 5. Measurements were performed for wavenumbers between 4000 cm −1 and 420 cm −1 . The HDPE vibrations are evident in each composite. The two peaks in the region between 2919 cm −1 and 2849 cm −1 represent the stretching vibration of -CH2 group. Peaks at 1467 cm −1 and 721 cm −1 represent the bending vibration and rocking deformation of the -CH2 group, respectively 22 . A small peak at 419 cm −1 was observed which is normally assigned to the stretching vibration of Mg-O 23,24 . It is interesting to note that Mg-O stretching vibration peak is more pronounced in the case of the composite containing 30 wt% of MgO when compared to that containing 5wt% MgO. However, this is as expected due to the increase in Mgo content in the composite.
The spectrometer consists of NaI (Tl) cylindrical detector of dimension (3˝ × 3˝) with relative efficiency 15% at the energy of Cs-137 (0.662 MeV).) and a lead-collimator with an inner diameter of 8 mm and an outer diameter of 100 mm was used as a house shield for the radioactive source, composite material, and detector. Plus, the source was placed at 508.67 mm from the attenuating sheets while the sheets were placed straight forward on the detector to verify very good geometry. The illustration of the experimental setup shown in Fig. 8 was measured for all discussed HDPE/MgO samples using a good geometry technique of gamma-ray spectroscopy in the radiation physics laboratory, faculty of science, Alexandria University. The collected spectra were analyzed by using Genie 2000 software. The counting time in each run for the same sample with a certain thickness was limited by the value of the statistical error in the peak area for the considered energy to be less than 1%. The previous step was repeated for all composite samples with varying thicknesses and for all considered energies where the count rate (N) was determined from the peak area divided by the counting time.
Shielding parameters. The count rate (N) was measured for all energies as a function of disc thickness (x) either for micro or nano MgO /HDPE samples. From the slope, LAC was calculated experimentally by the next equation 31,32 .
To confirm the validity of LAC values, LAC for HDPE loaded with micro filler were obtained from the XCOM software 33,34 compared with the experimental values. The relative deviation between the two values was calculated by: The other radiation attenuation parameters based on LAC calculations, such as half value layer (HVL), mean free path (MFP) and tenth value layer (TVL) were estimated from the following equations 35 .
The effect of chemical composition of shielding material was elucidated using the effective atomic number (Z eff ) which depends on the mass attenuation coefficient (µ/ρ) as shown in the following equation.
where (µ/ρ) i ,w i , A i and Z i are the mass attenuation coefficient , the weight fraction, the atomic weight and the atomic number respectively for constituent element in the sample. Additionally, the G-P fitting method 36  where R is defined as the ratio of mass attenuation coefficient by Compton effect and the total mass attenuation coefficient (μ comp /μ total ) for given shielding material and for all the elements. Z 1 and Z 2 are the atomic numbers of elements that correspond to the ratios R 1 and R 2 . The P stands for the G-P fitting parameters (b, c, a, X k and d) are used for the calculation of EABF and EBF, while P 1 and P 2 are the values of G-P fitting parameters that correspond to the atomic numbers Z 1 and Z 2 . In addition, E and x represent the incident photon energy and the mean free path's penetration depth, respectively.

Results and discussion
Mechanical results. To investigate the change in the mechanical properties of the HDPE due to the addition of micro and nano MgO oxide in different percentages. The dog-shaped samples were subjected to gradually increasing stresses while the produced strains were recorded and the results are depicted as shown in Fig. 9. It is very clear from the obtained results that the addition of MgO in any size will increase remarkably the ultimate force of the composite samples this increase is obvious at the concentration 5% for added MgO either for micro or nano but the composite samples loaded with 5% percent nano MgO could bearing more stresses than the 5% percent micro MgO. This could be explained based on the size of the particles inside the sample, where particles with nano size could be distributed uniformly inside the matrix of the composite to produce a specimen with higher cross linking in the case of nano than micro. Moreover, from the obtained results, the ultimate force is nearly the same for samples loaded with MgO with higher concentrations than the 5% MgO, which means the mechanical stability of the sample with added MgO is still better than the pure MgO.
Shielding results. The shielding properties of the prepared composites HDPE/ MgO were examined by using standard gamma point sources having energies between 0.06 and 0.1408 MeV, Fig. 10 shows the spectrum of Co-. The geometrical setup between the source, sample, and scintillation detector must verify the conditions of Beer-Lambert law. The calculated count rates (N) for HDPE samples loaded with micro MgO with concentrations (0,5,10,20 and 30% by weight) and nano-MgO with concentrations (5 and 30%) were determined by using software of Genie 2000 as function of sample thickness. All the data for all measurements were displayed on graphs where the Y-axis represents log(N) and X-axis represents the thickness X to get straight line, its www.nature.com/scientificreports/ slope =-linear attenuation coefficient µ (cm −1 ). Figure 11 depicts, for example, the curves for some HDPE samples loaded either with micro or nano MgO, where Table 1 gives all the shielding parameters for all samples and table (2) shows the relative increasing R(%) between the results of LAC of the micro and the results of nanofiller. It is clear from the example curves and the values of LAC mentioned in Tables 1 and 2 that the presence of MgO, either as micro or nano enhances the attenuation properties of HDPE at all used photon energies. Moreover, the attenuation of photons in nanocomposites was higher than that of micro composites at the same concentrations. A good question here is: why are these changes in the attenuation parameters? It is well known that the attenuation of photons inside any absorbing medium depends on the density, the atomic number of the medium, and the energy of the incident photons. Of course, the presence of MgO will increase both the density and the effective atomic number of the used composite in this work, which means that the electronic density of the absorbing medium will increase, and this in turn will increase the probabilities of interactions between the transmitting photons and the electrons. More interactions yield more energy loss and more attenuation. It is worthwhile mentioning that the distribution of nano particles inside the composite will help to increase these interactions and attenuation probabilities see Fig. 12. This illustration was confirmed by increasing the concentration of MgO either in micro or nano sizes where LAC values increase at any specific energy than those of pure HDPE. On the other hand, photon energy plays an important role in affecting the attenuation of photons where higher energies produce less attenuation because the Compton scattering within the range of the used photon energy in this work is predominant. Figure 13 displays the relation between the experimental values of LAC and those calculated from XCOM program composites loaded with micro MgO to see how true the experimental measurements are. An improvement    Figure 15 shows that the radiation protection efficiency (RPE) which measures the effectiveness of shielding material for radiation protection and can be calculated by using Eq. (12) is a function of the energy of gamma ray photon and also depends on the concentration of micro and nano sized MgO in the HDPE matrix. At an energy of 0.08 MeV, RPE increases from 30.37% in the case of HDPE/ 5% micro MgO to 44.58% in the case of HDPE/ 5% nano MgO. By increasing the concentration of nano MgO in HDPE matrix to 30%, RPE increased to 50.19%. By increasing the energy of incident photon to 0.661 MeV, the value of RPE increased from 20.69% in the case of 5% micro MgO to 21.76 in the case of 5%nano MgO but at 30% concentration of nano MgO, the value of RPE is 25.68% at high energy 1.408 MeV and the value of RPE increased from 11.70% in the case of 5% micro MgO to 13.77% in the case of 5%nano MgO. By increasing the concentration of nano MgO to 30% , the value of RPE increased to 16.98%. At low energy range as shown in Fig. 16 Figure 17 displays the effective atomic numbers (Z eff ) which are calculated by Eq. (6) at gamma-ray energies ranging from 59.3 to 1408.01 keV. It is clearly seen that, the values of Z eff for all samples vary with the range of atomic numbers, and the Z eff values of each sample decrease with increasing gamma ray energy. Also, it has been found that, the values of Z eff rise as the MgO content in HDPE compositions rises. The interactions with gamma rays in composite materials depend on their Z eff value and photon energy.
The energy absorption buildup factor (EABF) and exposure buildup factor (EBF) versus photon energy are shown in Figs. 18 and 19. EABFs and EBFs typically exhibit low values at low and high energies and high values at medium energies. In the studied energy range, photon interactions can be used to explain these corollaries. The photons are mostly annihilated or lose energy at low energy levels because the photoelectric effect is the predominant process. There is less photon buildup as a result. Then, all samples' EABFs and EBFs gradually

Conclusion
In this investigation, the effect of particle size and weight percentage of micro and nano MgO was determined by measuring the linear and mass attenuation coefficient of the HDPE/MgO composite at different photon energies. The compression molding technique was used to fabricate composites, and the morphological properties of composites were investigated by SEM. From SEM images, the distribution of nano MgO in the matrix is more uniform than micro MgO and also shows strong adhesion between the HDPE matrix and MgO. Adding MgO to the HDPE matrix led to a significant improvement in the mechanical and radiation properties of the composite. The ultimate force increased by increasing the concentration of micro MgO in the HDPE matrix led to an increase in the required force for the material to reach its ultimate point. Replacing micro MgO filler with nanofiller with low concentration led to additional improvement in the mechanical properties of the composite. RPE of composite also improved as the concentration of micro MgO increased, the mass attenuation coefficient increased at the same energy, and the HVL decreased significantly, and the ability of the HDPE/MgO composite improved by replacing micro MgO.